The present invention relates generally to hand-held rotary tools, and more particularly to the construction of, and/or the control of pressurized fluid flowing through, a rotary turbine tool.
Air motors are conventionally used to drive high speed hand-held rotary tools, such as grinders and drills, because the air motor is suitable for light work and relatively safe. Unfortunately, many air motors of the prior art have poor speed regulation, with speed tending to drop drastically in the face of torque loading. Efforts have been made to improve speed regulation, with less than ideal results. For instance, U.S. Pat. No. 3,071,115 to Schott discloses one prior art approach for controlling the speed of a pneumatic rotation motor. The Schott approach relies on mechanical flyweights for both a speed governor and an overspeed safety device. While both the Schott governor and the overspeed safety device are disposed within the motor, the Schott rotor design as a whole is rather complicated, requires a relatively large radial space, and is difficult to adapt to very fast rotating motors. Particularly in high speed applications, the centrifugal forces acting on the flyweights and other parts in the Schott design place high demands on the dimensions and material of the flyweight springs, etc., increasing costs.
More recently, U.S. Pat. No. 6,241,464 to Huffaker discloses a rotary turbine tool with an approach to speed control that relies on the interplay of a complex elastomeric valve member and a plurality of valve guides to control airflow, with no back-up form of overspeed protection.
Thus, there remains a need for alternate rotary tool designs, particularly for alternative hand-held rotary turbine tool designs.
The present invention provides an improved hand-held turbine tool design with a number of innovative aspects which may be incorporated into the tool individually or as a group. One aspect of the present invention relates to improved speed control based on an elastically deformable governor member disposed within the rotating impeller assembly and having a substantially uniform cross-section. Another aspect of the present invention relates to an overspeed safety configuration that employs secondary, or xe2x80x9cretroxe2x80x9d, nozzles that are enabled when the elastically deformable governor member is removed from the impeller assembly. Another aspect of the present invention relates to routing the motive fluid exhaust through the operator-adjustable throttle assembly. Still another aspect of the present invention relates to a simplified method of axially preloading the bearings supporting the rotating shaft of the impeller assembly.